A controller for a continuously variable transmission (CVT) for a vehicle disclosed in Tokkai Hei 8-74958 published by the Japanese Patent Office in 1996 sets a target speed ratio according to running conditions including a throttle opening, and controls the CVT so that the real speed ratio follows the target speed ratio.
This controller distinguishes between an auto upshift wherein the throttle opening is in an effectively constant state, upshift due to a decrease in degree of throttle opening, and downshift due to an increase in degree of throttle opening, based on a comparison of the target speed ratio with a real speed ratio and a variation of throttle opening. Based on the result of this distinction, a speed change response is changed.
When the speed change response is low in auto upshift, there is a possibility that the approach of the real speed ratio to the target speed ratio will be delayed, and engine rotation speed will rise excessively, and when the speed change response is high during upshift due to throttle opening decrease, the vehicle accelerates even though the accelerator pedal is returned, and gives an uncomfortable feeling to the driver.
Therefore, in this prior art device, the speed change response in upshift due to throttle opening decrease is set lower than the speed change response in auto upshift.
However, when the speed change response is set low like this, if the accelerator pedal is released from the substantially fully open state, there is a possibility that a deceleration shock will occur immediately after upshift starts. For example, when the accelerator pedal is depressed and the throttle opening is large, the real speed ratio increases together with engine rotation speed, and when the foot is released from the accelerator pedal in this state, fuel cut begins. If the speed change response is slow at this time, a deceleration shock occurs.